Sulfonylurea compounds having a fused heterocyclic ring are known as a herbicide having a high herbicidal activity and high safety for crops (e.g., see JP-B H05-36439 and JP-A H01-139582). Among them, a sulfonylurea compound having imidazo[1,2-b]pyridazine ring as a fused heterocyclic ring is one of compound groups having a high activity, especially the present inventors found out that a compound having a substituent bonded to the 6-position carbon atom of imidazo[1,2-b]pyridazine ring has a high herbicidal activity against weeds resistant to conventional sulfonylurea herbicides, and filed a patent application (JP Application No. 2003-6756). As a reaction for introducing a substituent at the 6-position carbon atom of imidazo[1,2-b]pyridazine ring, Journal of Antibiotics, 54 (3), 257-277, 2001; Synthesis, (4), 595-600, 2001; JP-A H05-271233; JP-A H06-116272; JP-A H11-310581; JP-A H11-310582; JP-A 2000-198735; JP-A 2001-199889 and the like are known.
The object of this invention is to provide a process for easily and inexpensively producing an imidazo[1,2-b]pyridazin-3-ylsulfonamide derivative having a substituent bonded to the 6-position carbon atom which is useful as a synthetic intermediate for herbicides.